1. Field of the Invention
This invention relates to a gloss measurement apparatus and gloss measurement method for emitting light from a light source and, on the basis of specular reflected light which is reflected by an object to be measured, finding an evaluation value which represents a degree of glossiness of the object to be measured.
2. Description of the Related Art
Gloss of a recording medium, and of images and text formed by an image recording device such as a color printer or the like, is a major factor in image quality, which greatly affects the high-quality feel of documents, readability of text and the like, and gloss is utilized as one of the parameters of quality control.
Heretofore, as a method for measuring gloss of a surface of an object, a specular gloss measurement method which projects light onto the surface and measures a reflected light amount in a specular reflection direction to find a degree of gloss value has been widely known (JIS-Z8741). This specular gloss measurement method is a measurement method in which parallel light is incident on an object to be measured at a prescribed incidence angle θ, light flux which has been reflected in the specular reflection direction from the object to be measured is detected by a light detector, and the reflected light flux that has been detected is normalized in accordance with reflected light flux that is detected under the same conditions with a standard surface (a glass surface with a refractive index of 1.567 over the range of visible wavelengths). For this specular gloss measurement method, measurement processes in which 20°, 45°, 60°, 75° and 85° are applied as the incidence angle θ are prescribed. In general, it is considered preferable to use measurement processes in which the incidence angle is small for measurement of objects to be measured with high gloss and measurement processes in which the incidence angle is large for measurement of objects to be measured with low gloss.
However, because the specular gloss value is an index representing a magnitude of reflected light flux in a specular reflection direction, a specular gloss value measured by the above-described specular gloss measurement method might not correspond to a degree of gloss value according to subjective evaluation by human vision (below referred to as subjective glossiness). In such a case, it is not possible to quantitatively find the subjective glossiness from the specular gloss value. Therefore, subjective glossinesses cannot be quantitively controlled, and problems could arise in control of quality.